I once tried for about 2 months parking 3 domains, didn't have so much traffic and of course low revenue...but i guess nothing is imposible if you try enough.
The best way to monetize parked domains is by having huge amounted of parked domains which generic names.Not all domains are good. Here are the few tips you need to do to buy domains. Look for keyword rich generic domains names – which can get index faster in Google and can get some organic search engine traffic. Use keyword tools like Wordtracker or overture keyword suggestion tool to find keyword which is generic and can get traffic to these domains. Look for expired domains this doesn’t not be generic terms but domains which is expired domains with traffic, check the link popularity of these expired domains with traffic so that these domains will still be getting good traffic and can earn money by parking these kinds of domains. To find expired domain names you can get it from snapnames.com, pool.com and networksolutions.com.